The invention relates to an article of footwear which has a dynamically changing motion control and cushioning bladder system. The bladder system provides varying amounts of resistance to side-to-side motion depending on the severity of such motion while walking, running, or participating in other athletic activities.
The typical running stride involves the runner landing on the lateral, posterior edge of the footwear in the heel region followed by pronation toward the medial side as the foot continues through its stride. As footstrike continues, the foot stops pronating and begins to supinate as the foot rocks forward so that the foot reaches a neutral position at midstance. From midstance, the foot rocks forward to the forefoot region where toe-off occurs at the ball and front of the foot. Toe-off typically involves the toes on the medial side of the foot pushing off the running surface as the foot leaves the ground to begin a new cycle.
Pronation involves the rolling of the foot from its lateral, posterior side to its inner, medial side. Although pronation is normal and necessary to achieve proper foot positioning, it can be a source of foot and leg injuries for runners who over pronate. The typical runner who over pronates lands on the outer, lateral side of the heel in a supinated position and then rolls medially across the heel toward the inner side of the footwear beyond a point which may be considered normal. While some amount of pronation is helpful in decreasing pressure and stress experienced by the leg, excessive pronation can cause stress on various joints, bones and soft tissue. Supinating, which involves rolling of the foot from the medial to the lateral side, while not as common as over pronating, can also cause foot and leg injuries if it is excessive.
Modern running and walking footwear are a combination of many elements each having a specific function which aids in the overall ability of the footwear to withstand many miles of running or walking, while providing cushioning and support for the foot and leg. Articles of athletic footwear are divided into two general parts, an upper and a sole. The upper is designed to snugly and comfortably enclose the foot, while the sole must provide traction, protection and a durable wear surface. It is often desirable to provide the footwear with a midsole having a layer of resilient, cushioning materials for enhanced protection and shock absorption when the heel strikes the ground during the stride of the wearer. This is particularly true for training or jogging footwear designed to be used over long distances or over a long period of time. These cushioning materials, must be soft enough to absorb the shock created by the foot strike and firm enough not to xe2x80x9cbottom outxe2x80x9d before the impact of the heel strike is totally absorbed.
Attempts have also been made to provide support and comfort in an article footwear by incorporating bladders in fluid communication with each other within a sole. Examples of these devices include U.S. Pat. No. 4,183,156 to Rudy (which is hereby incorporated by reference); U.S. Pat. No. 4,446,634 to Johnson et al.; U.S. Pat. No. 4,999,932 to Grim; Austrian Patent No. 200,963 to Schutz et al.; and HYDROFLOW(copyright)ST, by BROOKS(copyright) Sports, Inc.
Conventional running and walking footwear designed to provide the user with the maximum amount of available cushioning tend to sacrifice footwear stability by using a midsole cushioning system that is too soft and has too much lateral flexibility for a person who over pronates or requires some form of motion control. The lateral flexibility and deformation of traditional cushioning materials contribute to the instability of the subtalar joint of the ankle and increase the runner""s tendency to over pronate. This instability has been cited as one of the causes of xe2x80x9crunners kneexe2x80x9d and other such athletic injuries. As a result, over-pronators generally do not use contemporary shoes specifically designed for maximum cushioning, but instead use heavier, firmer footwear, or footwear having motion control devices specifically designed to correct physical problems such as excessive pronation. Motion control devices limit the amount and/or rate of subtalar joint pronation immediately following foot strike.
Various ways of resisting excessive pronation or instability of the subtalar joint have been proposed and incorporated into running footwear as motion control devices. In general, these devices have been fashioned by modifying conventional footwear components, such as the heel counter, and/or the midsole cushioning materials. Unlike the present invention, current motion control devices do not repeatedly adjust their level of support to match the varying degree of side-to-side motion accompanying each foot strike. Instead, when used to control pronation, devices such as firm medial posts limit over pronation by providing a substantially rigid structure with a constant stiffness and level of support that presses against the medial side of the foot, limiting internal rotation of the ankle. Examples of motion control devices include: U.S. Pat. No. 5,046,267, to Kilgore et al.; U.S. Pat. No. 5,155,927, to Bates et al.; and U.S. Pat. No. 5,367,791, to Gross et al.
Two of the most common reasons for foot and knee injuries sustained by runners and walkers are insufficient shock absorption and a lack of proper lateral motion control. Both reasons must be considered when designing footwear so the wearer receives the proper amount of cushioning and motion control without significantly increasing the overall weight of the footwear. Many runners who require a moderate amount of motion control may have to use heavy, bulky footwear, which is weighted down by support features, and designed for the severe over pronator.
The present invention introduces cushioning and dynamic motion control in a single, multi-bladder system providing optimum cushioning, while simultaneously providing the needed amount of motion control by stiffening a portion of the footwear in response to the individual user""s lateral motion, most frequently pronatory motion. The bladder system of the present invention takes into consideration the center-of-pressure pathway of the foot during typical footstrike to increase medial stiffness in response to lateral-to-medial rotation of the foot, so the more a user pronates, the stiffer the medial portion of the footwear is made. The bladder system provides comfort and control without the extra weight and bulk of prior art support structures because the support is provided by the flow of fluid in the cushioning system. The bladder system also provides a dynamically changing cushioning system that functions when pressure is applied to its region of the footwear and returns to equilibrium when the pressure is removed.
The present invention utilizes lightweight bladders for the dual purposes of cushioning and motion control. As a result, motion control footwear incorporating the present invention can be made lighter than its contemporary counterparts and provides a level of support commensurate with the degree of lateral motion, such as over-pronation, in each stride of the user.
An article of footwear for controlling side-to-side motion of a foot of a wearer according to the present invention comprises an upper, a sole attached to the upper, and a bladder system positioned within the sole of the footwear. The system includes at least first and second bladder chambers positioned side-by-side of one another and in fluid communication. A first valve is positioned between the first bladder chamber and the second bladder chamber. The first valve opens at a first predetermined level of pressure so that a fluid contained within the first outer bladder chamber is forced into the second bladder chamber when pressure within the first bladder chamber reaches the predetermined level to increase the pressure in the second bladder chamber and dynamically increase the support provided by the second bladder chamber on the side it is disposed.
In one preferred embodiment, the bladder system positioned is within a heel region of the sole and the first bladder chamber is disposed adjacent one side of the heel region, a third bladder chamber is disposed adjacent the other side of the heel region and the second bladder chamber is disposed between the first and third bladder chambers in fluid communication therewith. A second valve is positioned between the third bladder chamber and the second bladder chamber. The second valve includes a second pressure regulator that prevents fluid flow from the second bladder to the third bladder chamber when the pressure in the second bladder chamber is below a second predetermined pressure and allows fluid flow from the second bladder chamber to the third bladder chamber when the pressure in the second bladder chamber is at or above the second predetermined pressure to increase the pressure in the third bladder chamber and dynamically increase the support provided by the third bladder chamber.
The present invention also includes an embodiment which forces fluid from a central chamber into two outer chambers which surround it to stabilize the foot and prevent medial and lateral turning of the foot. In this embodiment, valves positioned within conduits connecting the chambers allow the contained fluid to immediately flow from the central chamber into the outer chambers when pressure is applied to the central chamber. In this embodiment, the direction of immediate fluid flow between the central chamber and the first outer chamber is opposite to that discussed above with respect to the other embodiments of the present invention. In this embodiment, fluid immediately flows from the central bladder to the two outer bladders when pressure is applied. Fluid only flows from the first outer bladder to the central bladder when it slowly bleeds back into it during the rest phase of the running or walking stride.